Interpretive Summary: Methicillin-Resistant Staphylococcus aureus (MRSA) causes severe human infections in clinical and community settings world-wide. Infections range from mild skin lesions to potentially fatal blood infections, regardless of an individual’s age or medical condition. More virulent strains are capable of producing Panton-Valentine leukocidin (PVL), which is a cytotoxin that targets white blood cells and causes tissue necrosis. These strains are usually associated with community-acquired MRSA (CA-MRSA). However, these virulent strains have been detected from ailing small companion animals and can potentially be transferred to human hosts. Also, MRSA has been isolated from healthy animals, where infections are not evident. Therefore, the purpose of the current study was to screen healthy cats and dogs for MRSA and characterize the type of strain(s) the animals carried. Sterile swabs and gauze were used to collect nasal, rectal, oral, abdomen and hindquarter samples from healthy animals at three veterinary clinics in the Athens, GA area. Staphylococcus aureus was isolated by standard methods and confirmed as MRSA using molecular methods. Antimicrobial resistance phenotype and genotype, PVL screening and specific molecular typing, such as multilocus sequence typing, was performed to determine the strain of MRSA isolated. Of the animals tested, 2% (6/276) were positive for MRSA. All isolates exhibited the same antimicrobial resistance profile, genotype and strain type. More importantly, all isolates were negative for PVL. These results suggest a single strain of MRSA may be carried by healthy animals. As such, consideration should be taken when handling healthy companion animals to reduce possible transfer of MRSA to human hosts. This study will be useful to veterinary personnel and others who routinely handle small companion animals by exposing possible risks of infection by MRSA.

Technical Abstract:
Methicillin-resistant Staphylococcus aureus (MRSA) is a significant human pathogen and has also been associated with wounded or ill companion animals. Healthy animals may also harbor MRSA without presenting any symptoms, but little is known about the prevalence of MRSA among these animals. Therefore, the current study describes MRSA isolated from healthy dogs and cats. Approximately 2% (6/276) of the animals tested were positive for MRSA. All MRSA isolates displayed the same resistance phenotype, genotype and harbored the mecA gene. In addition, ermA, which confers resistance to macrolides, lincosamides and streptogramin B, was also detected. Molecular typing revealed that all isolates were USA100, SCCmec type II, spa type t002 and ST 5. Panton-Valentine leukocidin (PVL) was not detected among the isolates. These results are consistent with those from previously reported characteristics of MRSA from healthy animals, suggesting that a specific strain of MRSA may be carried by healthy, asymptomatic animals. Such carriage poses an underlining risk of infection which should be considered during handling of healthy cats and dogs by pet owners and veterinary personnel.